Much like the stock market, no one knows what taxes will be in the future. So, saying one is better than the other is really just a guess.
Based on your current tax bracket you need to make an educated guess as to whether or not saving taxes upfront is more beneficial or not.
I'm in the 25% tax bracket, so I think that the traditional route is best for me, for both my 401k and IRA. I do contribute to a Roth IRA when I enter the phase out range for the IRA deduction.
My girlfriend on the other hand is only in the 15% bracket. So, its much more likely that a Roth will be of much more benefit to her than me. She also has less expendable income than me and contributes 7%, 6% for employer match and 1% to get the full savers credit, and we split that 4% to pre-tax 401k and 3% to her Roth 401k.
I think it's appropriate for everyone to have a little of both to maintain flexibility in retirement. And edge more toward Roth for low-income brackets.
JMHO